Carbon or graphite formed body

ABSTRACT

THIS INVENTION RELATES TO A CARBON OR GRAPHITE FORMED BODY, AND MORE PARTICULARLY AN ARC ELECTRODE HAVING A PROTECTIVE LAYER WHICH ARRESTS OXIDATION, AND WHICH INCLUDES A PRIMARY LAYER, APPLIED UPON A CARBON OR GRAPHIC FORMED BODY, AND A METALLIC COVER LAYER COMPRISED ESSENTIALLY OF ALUMINUM OVER THE PRIMARY LAYER. THE PRIMARY LAYER IS COMPRISED OF 90 TO 100%, PREFERABLY 95 TO 98.9%, OF SILCON AND 0 TO 10%, PREFERABLY 1.1 TO 5.0%, OF SODIUM, MAGNESIUM, CALCIUM, BORON, ALUMINUM, TITANIUM, ZIRCONIUM, MANGANESE, IRON, CARBON, NITROGEN PHOSPHORUS AND OXYGEN, SEPARATELY OR IN COMBINATION. THE COVER LAYER IS COMPRISED OF 85 TO 100%, PREFERABLY 93 TO 99.5%, ALUMINUM AND 0 TO 15%, PREFERABLY 0.5 TO 7%, SODIUM, MAGNESIUM, BORON, SILICON, PHOSPHORUS, OXYGEN, COPPER, ZINC, LEAD, TITANIUM, ZIRCONIUM, CHROMIUM, MANGANESE, IRON, COBALT AND NICKEL, SEPARATELY OR IN COMBINATION.

CARBGN R GRAPHZTE FORMED BODY ttrnar Rubisch, Meitingen, near Augsburg,Germany, assignor to Sigri Elel-rtrographit Gescllschatt mitbeschranltter lilaftung, Mcitingen, near Augsburg, Gerfective protectionagainst oxidation of the aforementioned formed body of graphite orcarbon. According to the 428 408e XR 395539010 SR 12 assault; a gPatented ,.laln. 5, 1971 invention, the primary layer is comprised of 90to 100%, 3,553,010

preferably 95 to 98.9%, of silicon and 0 to 10%, preferably 1.1 to 5%,of sodium, magnesium, calcium, boron. aluminum, titanium, zirconium,manganese, iron, carbon, nitrogen, phosphorus and oxygen, separately orin com- 5 an bmatron, and the cover layer of 85 to 100%, preferably ia llirgssi iig l il sd ifiiz? 719 08. Ser. No. 747,129 93 to 99.5%, ofaluminum and 0 to 15%, preferably 0.5 Claims priority, applicationGermany, July 26, 1967, to 7%, of sodium, magnesium, boron, SlilCOl'l,phosphorus,

1,571,055 oxygen, copper, zinc, lead, titanium, zirconium chro- B4431/20 mium manganese, iron, cobalt and nickel, separately or in 3 CL117-217 5 Claims combination. All percentages used in this applicationare by weight. 1 b ff 5 The a lication of such a double ayer may e eecte ABSTRACT OF THE DISCLOSURE in a kn ii'n manner by means of flameinjection. It is This invention relates to a carbon or graphite formedparticularly preferable to provide the primary layer with body, and m rp r y n rc el r ing a a layer thickness of 0.01 to 0.15 preferably p pgo protective layer which arrests oxidation, and which in- 0.1 rrrnm, andthe comm a thickness 033i cludes a primary layer, applied. upon a carbonor graphite Winn, preferably ill to 0.3 mm. formed body, and a metalliccover layer comprised essen- Wen such a proEE'tiVlfiYE-"r" is applied byflame injectial y of aluminum r the P y y The p y -2 tion, it is onlymechanically bound to the carbon or layer is comprised of 90 to 100%,preferably 95 to graphite formed body. It was found that when the thus 99%, of silicon and 0 to 10%, preferably 1.1 to 5.0%, coated bodies areheated above approximately 550 C., of Sodium, magnesium, Calcium, 13aluminum, titathe components of the double layer react with eachothernium, Zirconium, manganese, iron, carbon, nit ogen p to form a lowmelting, eutectic alloy which closes the phorus and oxygen, separatelyor in combination. The pores formed by the flame injection. Finally, Ialso found cover layer is'comprised of 85 to 100%, preferably 93 thatsilicon which is dissolved mainly in aluminum, reacts to 99.5%, aluminumand 0 to 15%, pref bly 0.5 to 7%, with the carbon of the fundamentalbody forming silicon sodium, magnesium, boron, silicon, phosphorus,oxygen, carbide when the operational temperature of the procopper, zinc,lead, titanium, zirconium, chromium, mantected parts exceeds about 550C. which leads to a tearg fi, irOXl, Cobalt and nickel, lfi y inflflfree and solid bond between the protective layer to the tion. carbonpart. This bond is resistant to temperature changes. Carbon or graphitebodies provided with such coatings have shown a long lasting excellentstability with respect My invention relates to a carbon or graphiteformed to oxidation, at approximately 1700 C., due to the aforebody, andmore particularly an arc electrode having a described alloying effect.During a particularly strong protective layer which arrests oxidation,and which inoxidation attack, the protective effect of the double layer"eludes a primary layer, applied upon a carbon or graphite upon the bodycan be increased by an additional melting formed. body, and a metalliccover layer, comprised essenof the already applied coating. This meltingis carried out tially of aluminum, over the primary layer. in a knownmanner by an argon are or a direct plasma Carbon or graphite formedbodies are very widely used burner. The subsequent melting of theprotective layers I in chemical and metallurgical arts because of theirexcelre ult in an elimination of the pores and in a chemical \X J lentmechanical and thermal qualities. Frequently, howanchoring, which leadsto a considerable improvement of ,1 ,yever. the burning err, whichoccurs in these materials at the protection againstburning olf.

? temperatures above 550 C. in an oxidizing atmosphere, A similaradditional increase of the protective action ;z is disturbing 5 may beobtained by sealing the metallic double layer with y ,f, It is kn wnthat burning Off of the carbon and graphite a coating of an aqueoussolution of -10 to 30% alkali bodies can be reduced by impregnation withphosphate. borate and/or phosphate and/0r silicate. ll This, b reducesihe burning Off y p r The effect of the cover layer is also heightenedthrough I tures up to approximately 1100 C. the fact that duringoperation of the arc furnace, the l t It is further known to reduce theburning Off through current load of the electrodes is so measured thatthe the utilization of clover layers on carbon or graphite cover layeris heatedio above its melting point or soften- 1,; bodies. It ispreferred to produce said cover layers of ing point. This counteracts anotherwise possible tear transition metal silicides. The effect of suchlayers comformation in the cover layer caused by a. dilference in theprised of transition metal silicides is limited, though, to thermalexpansion coefficients of the fundamental material high temperatureswithin a range of 1200 to 1700 C. and the cover layer, thus preventingincreased oxidation Furthermore, the application of said layers ispossible which is feasible inand near the tears. only by means ofexpensive techniques. It is also known In this type of operation, thecoating layers in the to apply double layer coatings upon carbon orgraphite total region between the electrode holder which serves asbodies. The base layer may be a carbide layer, e.g. a a current supplyand the are, are in a fluid or even in a silicon carbide layer, whilethe cover layer may either plastic state, so that no voltages whatsoevercan be proconstitute a layer of an oxide mixture or a metal or siliducedin the coating layer through the dilferent expan- .cide layer. But eventhese layers do not yet afford an adesions of the coating layer and thefundamental body. quate protection, since it was not possible,heretofore, to Previously formed tears are automatically sealed by theadjust the expansion coefficients of the body to be proplastic or fluidcoating layer. Therefore a breaking off of tected and the applied layer,to each other. in the aforethe applied protective layer is not possible.mentioned double layers, the melting point is so high that I found itparticularly advantageous to produce, using tears which form cannot berecovered by thellow of the aforementioned preferred method ofoperation, coatthe layer. As a result, the layer is undercut byoxidation ings of components which in a temperature range beand breaksoff. tween 600 and 1200 (3., preferably 700 to i000" (3., The Presentinvention, lhefefofa, has 85 an j t rfform melting eutectics and tomeasure the current load such that the melting point of the eutectic isat least obtained on the electrode surface.

The atoredescrihed invention will now be disclosed with some embodimentexamples.

EXAMPLE 1' A graphite electrode with a diameter of 450 mm. and a lengthof 2000 mm. is left to rotate at about 50 revolutions per minute,following the customary, accurately scaled turning oft", in a rotatinglathe. Two tlame injection elec rodes, arranged in sequence at adistance of 200 mm., uniformly coat the electrode surface (injection distance 100 mm.), first with an 0.05 mm. thick. primary layer of 98.5%silicon+0.8% Fe+0.5% Al+0.2% Ca and thereafter with an 0.15 mm. thickcover layer of 99% Al+0.7% Mg+0.3% Si.

When used in an arc furnace, electrodes coated in this manner result ina graphite saving of 25 to 35% compared to untreated electrodes.

EXAMPLE 2 A graphite crucible 200 mm. in diameter, 500 mm. high and with20 mm. wall thickness is slowly rotated on a turntable, e.g. at 30 rpm.An approximately 0.1 mm. thick primary layer of 95% Si+3% Ti+1.5%Fe+0.5% Al is applied by means of a powder fiame injection pistol. Thecoating which is still approximately 70 C. is injection coated with acover layer of 0.2 mm. thickness, comprised of 98.2% Al+1.5% Mg+0.3% Mn,by Using a wire flame injection pistol, The coated crucible issubsequently dipped briefly into a 20% sodium phospiate solution (pH 5)and thereafter dried. at 120 When employed to operate in a coppercasting installation, the above-described crucibles achieve a life spanwhich is 4 to 6 times longer than in untreated crucibles.

I claim:

1. Formed bodyof carbonor graphite having an oxidation arrestingprotective layer which encompasses a primary layer on the carbon orgraphite formed body and a metallic cover layer on the primary layer,said primary layer being comprised of 90 to 100% silicon and 0 to 10% ofsodium, magnesium, calcium, boron, aluminum, titanium, zirconium,manganese, iron, carbon, nitrogen, phosphorus and oxygen, separately orin combination, the cover layer being comprised of to 100% aluminum and0 to 15% sodium, magnesium, boron, silicon, phosphorus, oxygen, copper,zinc, lead, titanium, zirconium, chromium, manganese, iron, cobalt andnickel, separately or in combination.

2. The body of claim 1 wherein the primary layer comprises to 98.9%silicon and 1.1 to 5.0% of a material selected from. sodium, magnesium,calcium, boron, aluminum, titanium, zirconium, manganese, iron, carbon,nitrogen, phosphorus, oxygen and mixtures thereof and the cover layercomprises 93 to 99.5% aluminum and 0.5 to 7% sodium, magnesium, boron,silicon, phosphorus, oxygen, copper, zinc, lead, titanium, zirconium,chromium, manganese, iron, cobalt and nickel and mixtures thereof.

3. The body of claim 1, wherein the primary. layer has a ltgglgnessmmgltgfl 15 mrn and the cover layer has a thickness of 0.05150 M4;"Fheh6dybf claim 1, wherein the primary layer has a thickness of 0.02to 0.1 mm. and the cover layer has a thickness of 0.1 to 0.3 mm.

5. The body of claim 4, wherein a sealing layer consisting of alkaliborate, phosphate, silicate or mixtures thereof is on the cover layer.

References Cited UNITED STATES PATENTS 2,295,379 9/1942 Beck et a1117--223X 3,120,453 2/1964 Fitzer et a1. 117-217 3,348,929 10/1967Valtschev et a1. 1172l7X 3,390,013 6/1968 Rubisch 117-221X 3,476,58611/1969 Valtchev ct a1. 117-217X r ALFRED L. LEAVITT, Primary ExaminerC. K. WEIFFENBACH, Assistant Examiner US. Cl. XJR-

